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Anja Bretzler

Anja Bretzler

About Me

I am a post-doctoral researcher in the group of Dr. Michael Berg (contaminant hydrology). My main focus currently lies on the "Groundwater Assessment Platform" (GAP), a free online data platform for mapping, statistical modelling and information exchange concerning geogenic groundwater contamination.

Previously, I was a PhD candidate in the groups of Prof. Mario Schirmer (Hydrogeology) and Dr. Stephan Hug (Chemistry of water resources). I conducted research on geogenic arsenic contamination of groundwater in Burkina Faso, West Africa, a drinking water contaminant that poses a serious health threat to the population. Using large-scale statistical models, we delineated areas with an elevated probability of having arsenic-affected groundwater due to favourable geological conditions. This work culminated in an arsenic hazard map for Burkina Faso that supports local stakeholders in the supply of safe drinking water. Other parts of my PhD focused on the development and field testing of low-cost, low-tech treatment methods to remove arsenic from drinking water in remote rural communities. The project was a collaborative effort together with partners from the Institut International d’Ingénierie de l’Eau et de l’Environnement (2iE), Université Ouaga I Pr. Ki-Zerbo and the NGO "Le soleil dans la main".

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Projects

An integrated project that aimed to develop a generally applicable framework for the mitigation of geogenic contamination in groundwater used for drinking, in particular concerning arsenic and fluoride.

Arsenic contamination in groundwater from crystalline basement rocks in West Africa has only been documented in isolated areas and presents a serious health threat in a region already facing multiple challenges related to water quality and scarcity. We present a comprehensive dataset of arsenic concentrations from drinking water wells in rural Burkina Faso (n = 1498), of which 14.6% are above 10 μg/L. Included in this dataset are 269 new samples from regions where no published water quality data existed. We used multivariate logistic regression with arsenic measurements as calibration data and maps of geology and mineral deposits as independent predictor variables to create arsenic prediction models at concentration thresholds of 5, 10 and 50 μg/L. These hazard maps delineate areas vulnerable to groundwater arsenic contamination in Burkina Faso. Bedrock composed of schists and volcanic rocks of the Birimian formation, potentially harbouring arsenic-containing sulphide minerals, has the highest probability of yielding groundwater arsenic concentrations > 10 μg/L. Combined with population density estimates, the arsenic prediction models indicate that ~ 560,000 people are potentially exposed to arsenic-contaminated groundwater in Burkina Faso. The same arsenic-bearing geological formations that are positive predictors for elevated arsenic concentrations in Burkina Faso also exist in neighbouring countries such as Mali, Ghana and Ivory Coast. This study's results are thus of transboundary relevance and can act as a trigger for targeted water quality surveys and mitigation efforts.

The geogenic contamination handbook: addressing arsenic and fluoride in drinking water

In some groundwaters, arsenic and fluoride can reach concentrations that are hazardous to human health if geological and geochemical conditions favour the release of these contaminants. This can especially pose a problem in developing countries where water service providers already struggle with the provision of clean water. The Geogenic Contamination Handbook, released in January 2015, aims to provide concise guidelines for practitioners faced with the problem of geogenically contaminated drinking water in low- and middle-income countries. The handbook is a digital resource, with the reader benefitting from numerous weblinks and embedded documents giving additional information where relevant. The necessary steps needed for sustainable mitigation of arsenic or fluoride-contaminated drinking water are outlined. This includes information on water quality testing (e.g. how to plan a field survey), different water treatment options as well as practical guidelines on the integration of technical, institutional and sociological aspects of arsenic and fluoride mitigation.

Groundwater origin and flow dynamics in active rift systems – a multi-isotope approach in the Main Ethiopian Rift

This study aims to investigate groundwater recharge and flow patterns in tectonically active rift systems, exemplified by a case study in the Main Ethiopian Rift. The chosen approach includes the investigation of hydrochemical parameters and environmental isotopes (3H, δ2H, δ18O, δ13C-DIC, 14C-DIC, 87Sr/86Sr). Apparent groundwater ages were determined by radiocarbon dating after correction of 14C-DIC using a modified δ13C-mixing model and further validation using geochemical modelling with NETPATH. Hydrochemical and isotopic data indicate an evolutionary trend existing from the escarpments towards the Rift floor. Groundwater evolves from tritium-containing and hence recently recharged Ca–HCO3-type water on the escarpments to tritium-free Na–HCO3 groundwater dominating deep Rift floor aquifers. Correspondingly, rising pH and HCO3– values coupled with increasingly enriched δ13C signatures point to hydrochemical evolution of DIC and beginning dilution of the carbon isotope signature by other carbon sources, related to a diffuse influx of mantle CO2 into the groundwater system. Especially thermal groundwater sampled near the most recent fault zones in the Fantale/Beseka region displays clear influence of mantle CO2 and increased water-rock interaction, indicated by a shift in δ13C and 87Sr/86Sr signatures. The calculation of apparent groundwater ages revealed an age increase of deep groundwater from the escarpments to the Rift floor, complying with hydrochemical evolution. Within the Rift, samples show a relatively uniform distribution of apparent 14C ages of ~1800 to ~2800 years, with the expected down-gradient aging trend lacking, contradicting the predominant intra-rift groundwater flow described in existing transect-based models of groundwater flow. By combining hydrochemical and new isotopic data with knowledge of the structural geology of the Rift, we improve the existing groundwater flow model and propose a new conceptual model by identifying flow paths both transversal and longitudinal to the main Rift axis, the latter being strongly controlled by faulted and tilted blocks on the escarpment steps. The connection between groundwater flow and fault direction make this model applicable to other active rift systems with similar structural settings.